The NameNotFoundException is the clue. I bet you have a problem with your classloader / classpath.
This article "TroubleShooting: Classloader problems for WebSphere Application Server"
http://www.IBM.com/support/docview.wss?rs=180&uid=swg21219358 does a pretty good job of helping with many/most of this kind of issue.
Take a look and see if it helps you, and let me know.